The present invention relates to photovoltaic devices and more particularly to photovoltaic devices having improved carrier collection efficiency.
It is well known to those in the photovoltaic art that radiation at the higher wavelength portion of the solar spectrum must travel farther through a body of semiconductor material in order to be absorbed. The farther into the semiconductor body radiation must travel in order to be absorbed, the longer the carrier diffusion length should be to assure collection of the generated carriers at a P-N junction. Semiconductor materials which are of poor crystalline quality, e.g., polycrystalline and amorphous semiconductor materials, have diffusion lengths of generated carriers which are relatively short. Thus photovoltaic devices of a thickness sufficient to absorb the high wavelength portion of the solar spectrum could not be fabricated utilizing these semiconductor materials. These semiconductor materials are cheaper to fabricate than the higher quality semiconductor materials, e.g., single crystalline silicon. Thus, it would be most desirable to have a photovoltaic device, and especially a solar cell, which had an improved collection efficiency so that the poor quality semiconductor materials can be used more practically. Also, such a photovoltaic device would improve the effectiveness of higher quality semiconductor materials.